1. Field of the Invention
The present invention relates to methods and algorithms for controlling robotic arms, and particularly to a method and algorithm for controlling a robotic arm having two links, a spherical wrist and seven degrees of freedom.
2. Brief Description of the Prior Art
Methods for controlling robotic systems, including robotic arms having several degrees of freedom, can involve the utilization of complex algorithms requiring large computerized resources for computation and control. This is particularly true for robotic arms that are configured for space applications, which involve many considerations not present in terrestrial applications. Safety and versatility are of prime importance in space applications. For example, safety concerns create a need for obstacle avoidance algorithms. Versatility demands may necessitate the manipulator's ability to perambulate between locations. Redundant manipulators meet these requirements because the additional degrees of freedom allow inclusion of obstacle avoidance algorithms and increase the maneuverability of the manipulator. The redundant joint configuration described in the present application consists of two links with identical two degree-of-freedom "shoulder" and "elbow" joints and a spherical "wrist" making a total of seven degrees of freedom. This particular joint geometry has favorable characteristics with respect to singularity avoidance, obstacle avoidance and simplicity. The present robotic arm utilizes a spherical wrist having three degrees of freedom, such that its kinematics are decoupled from the two links of the arm.
U.S. Pat. No. 4,794,547, issued Dec. 27, 1988 to Azusa Nishida, and U.S. Pat. No. 4,823,279, issued Apr. 18, 1989 to William Perzley et al., both depict a two link robotic arm having a wrist-like end effectuator engaged therewith. These patents present systems and algorithms for the manipulation of the robotic arm described therein. These inventions fail to achieve the versatility and simplicity of the present invention in that the end effector lacks three degrees of freedom and is therefore not decoupled from the two links of the arm. Additionally, the two links do not possess four degrees of freedom, whereby redundancy of motion is not achieved in the arm, and consequently the versatility of the present invention is not achieved. U.S. Pat. No. 4,772,831, issued Sept. 20, 1988 to Casler, Jr. et al.; U.S. Pat. No. 4,763,276, issued Aug. 9, 1988 to Perreirra et al.; and U.S. Pat. No. 4,680,519, issued July 14, 1987 to Chand et al., teach more generalized control systems for robotic arms having a plurality of links and/or joints.
U.S. Pat. No. 4,794,540, issued Dec. 27, 1988 to Gutman et al.; U.S. Pat. No. 4,725,942, issued Feb. 16, 1988 to Osuka; U.S. Pat. No. 4,672,564, issued June 9, 1987 to Egli et al.; U.S. Pat. No. 4,655,352, issued May 12, 1987 to Bartelt et al., each teach generalized control systems for robotic arms.